Sheet processing device and image forming system

ABSTRACT

A sheet processing device is for binding sheets together. The sheet processing device includes binding units differing from each other in maximum sheet count, the maximum sheet count being a maximum number of sheets that can be bound at a time; a sheet tray configured to hold sheets until all to-be-bound sheets are placed therein, the number of the to-be-bound sheets being a largest one of the maximum sheet counts of the binding units or smaller; and a stacked-sheet-count limiting unit situated in a thickness direction of the sheets held in the sheet tray. The stacked-sheet-count limiting unit is configured to limit the number of sheets held in the sheet tray by varying a distance from a sheet support surface of the sheet tray on which the sheets are placed, depending on one of the binding units by which the sheets held in the sheet tray are to be bound.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and incorporates by referencethe entire contents of Japanese Patent Application No. 2014-123687 filedin Japan on Jun. 16, 2014.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a sheet processing device andan image forming system and, more particularly, to sheet binding.

2. Description of the Related Art

Increasing digitization of information in recent years has made imageprocessing apparatuses such as printers and facsimiles for use inoutputting digitized information and scanners for use in digitalizingdocuments indispensable. Such an image processing apparatus is typicallyconfigured as a multifunction peripheral (MFP) having an image capturefunction, an image forming function, a communication function, and thelike and usable as a printer, a facsimile, a scanner, and a copier.

It is known that some type of MFPs is equipped with a binding devicethat binds a bundle of a plurality of sheets, on which images are formedby the MFP, together. Schemes used by such a binding device in binding asheet bundle include a scheme (hereinafter, “staple binding”) with useof a metal staple(s) and a scheme (hereinafter, “stapleless binding”)without use of a metal staple.

As such a binding device as that described above, a binding devicecapable of both staple binding and stapleless binding has been proposedand known. An example is disclosed in Japanese Laid-open PatentApplication No. 2004-168435. Binding devices capable of both the schemesare typically configured to perform binding as follows. First, aselected one of a staple binding unit that performs staple binding and astapleless binding unit that performs stapleless binding is moved fromits home position to a binding position. The binding device thenreceives a sheet bundle into a binding channel of the moved binding unitand sandwiches the received sheet bundle from above and below sheetsurfaces, thereby binding the sheet bundle.

Some type of the binding devices capable of both the schemes isconfigured such that the maximum number of sheets (hereinafter, “maximumsheet count”) that can be bound at a time by staple binding differs fromthat of stapleless binding. In some binding devices of this type, acompiling unit where sheets are to be stacked in a pile until allto-be-bound sheets are placed therein is designed to have a heightadjusted to a larger one of the maximum sheet counts. A binding deviceconfigured in this manner can stack, even if the maximum sheet countsdiffer between staple binding and stapleless binding, a correspondingmaximum sheet count of sheets for each of the schemes.

However, when the compiling unit of the binding device is designed tohave a height adjusted to a larger one of the maximum sheet counts, thefollowing disadvantage can occur. When a sheet bundle is to be boundusing one, which is smaller in the maximum sheet count, of the schemes,even if the sheet bundle contains the maximum sheet count of sheets, aclearance in the direction of sheet thickness is left in the compilingunit. The clearance can cause curling, deflection, or the like to occurin the sheet bundle at a binding position. Accordingly, the bindingdevice configured as described above can have the following problem.When a sheet bundle is to be bound using the one, which is smaller inthe maximum sheet count, of the schemes, even if the sheet bundlecontains the maximum sheet count of stacked sheets or less, the curlingor deflection described above can increase the thickness of the sheetbundle relative to the thickness of the sheet bundle free from thecurling, deflection, or the like (hereinafter, “should be thickness”) toexceed opening height of the binding channel. As a result, the sheetbundle cannot be received into the binding channel.

A method of pressing the sheet bundle stacked in the compiling unit ofthe binding device in the direction of sheet thickness may beapplicable. Examples of this method are disclosed in Japanese Laid-openPatent Publication No. 2005-263404 and Japanese Laid-open PatentPublication No. 10-279163. When the binding device is configured toapply this method, occurrence of the curling, deflection, or the likecan be reduced even if a clearance in the sheet thickness direction isleft in the compiling unit.

However, such a binding device has a disadvantage that arises from theneed of pressing a sheet bundle stacked in the compiling unit in thesheet thickness direction. That is, a pressing member that presses thesheet bundle can interfere with sheet conveyance. This disadvantage canbe avoided by configuring the binding device to include compiling unitsindependently, one for staple binding and the other for staplelessbinding. However, this configuration disadvantageously increasesmanufacturing cost and device size due to an increase in the number ofparts and control systems.

Therefore, there is a need for a sheet processing device capable ofbinding sheets without interfering with sheet conveyance with aninexpensive, compact, and simple configuration.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an embodiment, there is provided a sheet processing devicefor binding a plurality of sheets together. The sheet processing deviceincludes a plurality of binding units differing from each other inmaximum sheet count, the maximum sheet count being a maximum number ofsheets that can be bound at a time; a sheet tray configured to holdsheets until all to-be-bound sheets are placed therein, the number ofthe to-be-bound sheets being a largest one of the maximum sheet countsof the plurality of binding units or smaller; and a stacked-sheet-countlimiting unit situated in a thickness direction of the sheets held inthe sheet tray. The stacked-sheet-count limiting unit is configured tolimit the number of sheets held in the sheet tray by varying a distancefrom a sheet support surface of the sheet tray on which the sheets areplaced, depending on one of the binding units by which the plurality ofsheets held in the sheet tray are to be bound.

According to another embodiment, there is provided an image formingsystem that includes an image forming apparatus configured to formimages on a sheet; and the sheet processing device according to theabove embodiment to bind a plurality of sheets together, an image isformed on each sheet by the image forming apparatus.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating an overall configuration ofan image forming apparatus according to an embodiment of the presentinvention;

FIG. 2 is a block diagram schematically illustrating a hardwareconfiguration of the image forming apparatus according to theembodiment;

FIG. 3 is a block diagram schematically illustrating a functionalconfiguration of the image forming apparatus according to theembodiment;

FIG. 4 is a perspective view of a sheet binding engine according to theembodiment;

FIG. 5 is a plan view of the sheet binding engine according to theembodiment;

FIG. 6 is a side view, as viewed along the main-scanning direction, ofthe sheet binding engine according to the embodiment;

FIG. 7 is a diagram illustrating size relation among height of acompiling unit, opening height of a staple binding unit, and openingheight of a stapleless binding unit according to the embodiment;

FIG. 8 is a perspective view of the sheet binding engine according tothe embodiment;

FIG. 9 is a plan view of the sheet binding engine according to theembodiment;

FIG. 10 is a side view, as viewed along the sub-scanning direction, of asheet bundle bound by the staple binding unit according to theembodiment;

FIG. 11 illustrates side views, as viewed along the main-scanningdirection, of the stapleless binding unit according to the embodiment;

FIG. 12 is a perspective view of the sheet binding engine according tothe embodiment;

FIG. 13 is a plan view of the sheet binding engine according to theembodiment;

FIG. 14 is a side view, as viewed along the sub-scanning direction, of asheet bundle bound by the stapleless binding unit according to theembodiment;

FIG. 15 is a side view, as viewed along the main-scanning direction, ofthe sheet binding engine according to the embodiment;

FIG. 16 is a side view, as viewed along the main-scanning direction, ofthe sheet binding engine according to the embodiment;

FIG. 17 illustrates side views, as viewed along the main-scanningdirection, of the sheet binding engine not including a movable guideplate according to the embodiment;

FIG. 18 illustrates side views, as viewed along the main-scanningdirection, of the sheet binding engine not including the movable guideplate according to the embodiment; and

FIG. 19 illustrates side views, as viewed along the main-scanningdirection, of the sheet binding engine according to the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described in detailbelow with reference to the accompanying drawings. As a particularexample, an image forming apparatus including a sheet binding unit thatbinds a plurality of sheets of media or the like together according toan embodiment is described below.

The sheet binding unit according to the embodiment is configured to becapable of, as schemes for binding a plurality of sheets together, botha scheme with use of a metal staple(s) (hereinafter, “staple binding”)and a scheme without use of a metal staple (hereinafter, “staplelessbinding”).

The sheet binding unit according to the embodiment is configured suchthat a maximum number of sheets (hereinafter, “maximum sheet count”)that can be bound at a time by staple binding differs from that ofstapleless binding. For this reason, a compiling unit where sheets areto be stacked in a pile until all to-be-bound sheets are placed thereinis designed to have a height adjusted to a larger one of a first maximumsheet count, which is the maximum sheet count of staple binding, and asecond maximum sheet count, which is the maximum sheet count ofstapleless binding. Accordingly, the sheet binding unit according to theembodiment, in which the first maximum sheet count of staple bindingdiffers from the second maximum sheet count of stapleless binding, iscapable of stacking a corresponding maximum sheet count of sheets foreach of staple binding and stapleless binding.

The sheet binding unit according to the embodiment is configured tooperate as follows. In a pre-sheet-binding phase, a staple binding unitthat performs staple binding and a stapleless binding unit that performsstapleless binding are on standby at their home positions. When sheetbinding starts, a selected one of the staple binding unit and thestapleless binding unit is moved from its home position to a bindingposition. The sheet binding unit according to the embodiment isconfigured to receive a sheet bundle into a binding channel of the movedbinding unit and sandwich the received sheet bundle from above and belowsheet surfaces, thereby binding the sheet bundle.

However, the sheet binding unit configured in this manner can have thefollowing disadvantage. When a sheet bundle is to be bound using one,which is smaller in the maximum sheet count, of the schemes, even if thesheet bundle contains the maximum sheet count of stacked sheets, aclearance in the sheet thickness direction is left. As a result,curling, deflection, or the like can occur at binding position.Accordingly, the sheet binding unit configured as described above canhave the following problem. When a sheet bundle is to be bound using theone, which is smaller in the maximum sheet count, of the schemes, evenif the sheet bundle contains the maximum sheet count of stacked sheetsor less, the thickness of the sheet bundle is increased relative to thethickness of the sheet bundle free from the curling, deflection, or thelike (hereinafter, “should be thickness”) to exceed the opening heightof the binding channel. As a result, the sheet bundle cannot be receivedinto the binding channel.

Under the circumstances, the sheet binding unit according to theembodiment is configured to include a movable guide plate whose heightin the sheet thickness direction varies depending on the maximum sheetcount or, more specifically, whose height in the sheet thicknessdirection varies depending on by which one of the staple binding unitand the stapleless binding unit a sheet bundle is to be bound.Accordingly, in the sheet binding unit according to the embodiment, evenif the curling, deflection, or the like occurs due to a clearancecreated in the thickness direction of sheets stacked in the compilingunit, the thickness of the sheet bundle does not exceed the movableguide plate.

By virtue of this configuration, when the sheet binding unit accordingto the embodiment performs sheet binding using one, which is smaller inthe maximum sheet count, of the schemes, even if the curling,deflection, or the like occurs due to a clearance left in the thicknessdirection of sheets stacked in the compiling unit, the thickness of thesheet bundle does not exceed the opening height of the binding channel.As a result, an undesirable situation that the sheet bundle cannot bereceived into the binding channel is prevented.

Hence, the sheet binding unit according to the embodiment can reliablyreceive a sheet bundle even when the sheet binding unit does not includecompiling units independently, one for staple binding and the other forstapleless binding, and the sheet bundle is to be bound using one, whichis smaller in the maximum sheet count, of the schemes. The sheet bindingunit according to the embodiment can be inexpensively manufactured andperform sheet binding with a compact and simple configuration.

An overall configuration of an image forming apparatus 1 according tothe embodiment is described below with reference to FIG. 1. FIG. 1 is asimplified diagram illustrating the overall configuration of the imageforming apparatus 1 according to the embodiment. As illustrated in FIG.1, the image forming apparatus 1 according to the embodiment includes animage forming unit 2, a sheet feeding unit 3, a sheet binding unit 4,and a scanner unit 5.

The image forming unit 2 generates CMYK (cyan, magenta, yellow, andblack planes) print information from input image data, and forms(outputs) an image on a sheet fed from the sheet feeding unit 3according to the generated print information. The sheet feeding unit 3feeds sheets, one at a time, to the image forming unit 2. The sheetbinding unit 4 performs sheet binding on a plurality of image-formedsheets conveyed from the image forming unit 2. In the sheet binding unit4 according to the embodiment, the maximum number of sheets that can bebound at a time (the first maximum sheet count) by staple bindingdiffers from that (the second maximum sheet count) of stapleless bindingsuch that the number of sheets that can be bound at a time by staplebinding is larger than that by stapleless binding. This configuration ofbinding mechanism included in the sheet binding unit 4 is a feature ofthe embodiment. In the embodiment, the sheet binding unit 4 functions as“sheet processing device”.

The scanner unit 5 digitizes an original document (hereinafter,“original”) by reading the original with a linear image sensor includinga plurality of linearly-arranged photodiodes and a light-receivingdevice such as a CCD (charge coupled device) image sensor or a CMOS(complementary metal oxide semiconductor) image sensor arranged parallelto the photodiodes. The image forming apparatus 1 according to theembodiment is a multifunction peripheral (MFP) having an image capturefunction, an image forming function, a communication function, and thelike and usable as a printer, a facsimile, a scanner, and a copier.

A hardware configuration of the image forming apparatus 1 according tothe embodiment is described below with reference to FIG. 2. FIG. 2 is ablock diagram schematically illustrating the hardware configuration ofthe image forming apparatus 1 according to the embodiment. The imageforming apparatus 1 includes, in addition to hardware elementsillustrated in FIG. 2, engines for performing functions as the scannerand the printer, sheet folding, sheet binding, and the like.

As illustrated in FIG. 2, the image forming apparatus 1 according to theembodiment includes elements similar to those of a typical server, a PC(personal computer), or the like. More specifically, the image formingapparatus 1 according to the embodiment includes a CPU (centralprocessing unit) 10, a RAM (random access memory) 20, a ROM (read onlymemory) 30, an HDD (hard disk drive) 40, and an I/F 50 that areconnected to each other via a bus 90. An LCD (liquid crystal display)60, an operation unit 70, and dedicated devices 80 are connected to theI/F 50.

The CPU 10, which is a processor, provides overall control of the imageforming apparatus 1. The RAM 20, which is a volatile storage medium toand from which information can be written and read out at high speeds,is used as a working area for information processing by the CPU 10. TheROM 30, which is a read-only non-volatile storage medium, storesprograms such as firmware. The HDD 40, which is a non-volatile storagemedium to and from which information can be written and read out, storesan OS (operating system), various control programs, applicationprograms, and the like.

The I/F 50 connects the bus 90 to various hardware, a network, and thelike and controls the connection. The LCD 60 is a visual user interfacethat allows a user to check a condition of the image forming apparatus1. The operation unit 70 is a user interface such as a keyboard and/or amouse for use by a user in inputting information to the image formingapparatus 1.

The dedicated devices 80 are hardware for performing functionsrespectively dedicated to the image forming unit 2, the sheet feedingunit 3, the sheet binding unit 4, and the scanner unit 5. The dedicateddevice 80 for the image forming unit 2 is a plotter that forms (outputs)an image on a surface of a sheet media. The dedicated device 80 for thesheet feeding unit 3 is a sheet feeding mechanism that feeds sheets, oneat a time, to the image forming unit 2.

The dedicated device 80 for the sheet binding unit 4 is the bindingmechanism that performs sheet binding on a plurality of sheets on whichimages are formed by the image forming unit 2. The configuration of thebinding mechanism included in the sheet binding unit 4 is a feature ofthe embodiment. The dedicated device 80 for the scanner unit 5 is areading device that reads an image displayed on a surface of a sheetmedia.

With the hardware configuration described above, a program stored in astorage device such as the ROM 30, the HDD 40, or an optical disk (notshown) is loaded onto the RAM 20. The CPU 10 executes processing inaccordance with the program loaded onto the RAM 20, thereby generatingsoftware control modules. Functional blocks that perform the functionsof the image forming apparatus 1 according to the embodiment areimplemented in a combination of the software control modules generatedas described above and hardware.

A functional configuration of the image forming apparatus 1 according tothe embodiment is described below with reference to FIG. 3. FIG. 3 is ablock diagram schematically illustrating the functional configuration ofthe image forming apparatus 1 according to the embodiment. In FIG. 3,electrical connections are indicated by solid lines with arrow heads;flows of a sheet or document bundle are indicated by dashed lines witharrow heads.

As illustrated in FIG. 3, the image forming apparatus 1 according to theembodiment includes a controller 100, a print engine 200, a sheetfeeding table 300, a sheet binding engine 400, a scanner engine 500, anADF (automatic document feeder) 600, a paper ejection tray 700, adisplay panel 800, and a network I/F 900. The controller 100 includes amain controller 101, an engine controller 102, an input/outputcontroller 103, an image processor 104, and an operation-and-displaycontroller 105.

The print engine 200, which is an image forming part included in theimage forming unit 2, prints an image by forming (outputting) an imageon a sheet conveyed from the sheet feeding table 300. Specific examplesof the print engine 200 include an inkjet image forming mechanism and anelectrophotographic image forming mechanism. An image-formed sheet,which is a sheet on which an image is printed by the print engine 200,is either conveyed to the sheet binding unit 4 or ejected onto the paperejection tray 700. The sheet feeding table 300, which is a sheet feedingpart included in the sheet feeding unit 3, feeds sheets, one at a time,to the print engine 200 which is the image forming part.

The sheet binding engine 400 included in the sheet binding unit 4performs sheet binding on image-formed sheets conveyed from the printengine 200. The sheet binding engine 400 according to the embodiment isconfigured to be capable of both staple binding and stapleless binding.In the sheet binding engine 400 according to the embodiment, the maximumnumber of sheets that can be bound at a time (the first maximum sheetcount) by staple binding differs from that (the second maximum sheetcount) of stapleless binding such that the number of sheets that can bebound at a time by staple binding is larger than that by staplelessbinding. The sheets bound by the sheet binding engine 400 are ejectedonto the paper ejection tray 700. The configuration of the bindingmechanism included in the sheet binding engine 400 is a feature of theembodiment.

The ADF 600 included in the scanner unit 5 automatically conveys anoriginal to the scanner engine 500 which is an original reading part.The scanner engine 500 included in the scanner unit 5 is the originalreading part including a photoelectric converter that converts opticalinformation into electrical signals. The scanner engine 500 reads anoriginal automatically conveyed thereto by the ADF 600 or an originalplaced on a platen glass (not shown) by optically scanning the originaland generates image information. The original automatically conveyed tothe scanner engine 500 by the ADF 600 and read by the scanner engine 500is ejected onto a paper ejection tray built in the ADF 600.

The display panel 800 is not only an output interface that providesvisual display of a condition of the image forming apparatus 1 but alsoan input interface used by a user in directly operating the imageforming apparatus 1 or entering information to the image formingapparatus 1. More specifically, the display panel 800 has a function ofdisplaying images for receiving operations made by a user. The displaypanel 800 is implemented in the LCD 60 and the operation unit 70illustrated in FIG. 2.

The network I/F 900 is an interface that allows the image formingapparatus 1 to communicate with other equipment such as anadministrator's terminal via a network.

As the network I/F 900, an interface such as Ethernet (registeredtrademark), USB (universal serial bus), Bluetooth (registeredtrademark), Wi-Fi (wireless fidelity), or FeliCa (registered trademark)may be used. The network I/F 900 is implemented in the I/F 50illustrated in FIG. 2.

The controller 100 is implemented in a combination of software andhardware. More specifically, a control program such as firmware storedin a non-volatile storage medium such as the ROM 30 or the HDD 40 isloaded onto the RAM 20. The CPU 10 executes processing in accordancewith the program loaded onto the RAM 20, thereby generating softwarecontrol modules. The controller 100 is implemented in the softwarecontrol modules and hardware such as an integrated circuit. Thecontroller 100 functions as a control part that provides overall controlof the image forming apparatus 1.

The main controller 101 performs a function of controlling the blocksincluded in the controller 100 and feeds commands to the blocks of thecontroller 100. The main controller 101 controls the input/outputcontroller 103 to access other equipment via the network I/F 900 and anetwork. The engine controller 102 controls drivers of the print engine200, the sheet feeding table 300, the sheet binding engine 400, thescanner engine 500, and the like or causes the drivers to drive thesame. The input/output controller 103 feeds signals and commands inputthereto via the network I/F 900 and a network to the main controller101.

The image processor 104 generates, under control of the main controller101, print information from document data or image data contained in aninput print job. The print information is data, such as CMYK bitmapdata, according to which the print engine 200, which is the imageforming part, prints an image by performing an image forming operation.Furthermore, the image processor 104 generates image data by processingcaptured image data fed from the scanner engine 500. The image data isinformation stored in the image forming apparatus 1 or transmitted toother equipment via the network I/F 900 and a network as a result of ascanner operation. The operation-and-display controller 105 displaysinformation on the display panel 800 or notifies the main controller 101of information entered via the display panel 800.

A configuration of the sheet binding unit 4 according to the embodimentis described below with reference to FIGS. 4 to 6. FIG. 4 is aperspective view of the sheet binding engine 400 according to theembodiment. FIG. 5 is a plan view of the sheet binding engine 400according to the embodiment. FIG. 6 is a side view, as viewed along themain-scanning direction, of the sheet binding engine 400 according tothe embodiment.

As illustrated in FIGS. 4 to 6, the sheet binding engine 400 accordingto the embodiment includes a compiling unit 410, a staple binding unit420, a staple-binding-unit guide rail 421, a staple-binding-unitdetection sensor 422, a stapleless binding unit 430, astapleless-binding-unit guide rail 431, a stapleless-binding-unitdetection sensor 432, a sheet support plate 440, registration guides450, a movable guide plate 460, and a movable-guide-plate pivot-supportmember 461.

The compiling unit 410 holds sheets in a pile until all to-be-boundsheets are placed therein. Put another way, the compiling unit 410 holdssheets until all of the plurality of to-be-bound sheets are placedtherein. The number of the to-be-bound sheets is equal to or smallerthan a larger one of the maximum sheet count of the staple binding unit420 and that of the stapleless binding unit 430. In other words, in theembodiment, the compiling unit 410 functions as “sheet tray”.

The compiling unit 410 according to the embodiment is designed to have aheight H in the sheet thickness direction adjusted to the larger one ofthe maximum sheet count of staple binding and that of staplelessbinding; in short, the height H is adjusted to staple binding. Hence,the compiling unit 410 is configured to have the height H in the sheetthickness direction that is equal to an opening height L₁ of a bindingchannel of the staple binding unit 420 as illustrated in FIG. 7.

Accordingly, in the embodiment, the following relation holds: H=L₁>L₂,where H is the height of the compiling unit 410 in the sheet thicknessdirection, L₁ is the opening height of the binding channel of the staplebinding unit 420, and L₂ is an opening height of a binding channel ofthe stapleless binding unit 430. FIG. 7 is a diagram illustrating sizerelation among the height H of the compiling unit 410 in the sheetthickness direction, the opening height L₁ of the binding channel of thestaple binding unit 420, and the opening height L₂ of the bindingchannel of the stapleless binding unit 430.

In a pre-sheet-binding phase, the staple binding unit 420 is on standbyat its home position. When sheet binding starts, the staple binding unit420 moves from the home position to a binding position on thestaple-binding-unit guide rail 421. The staple binding unit 420 binds asheet bundle 6 by inserting a staple A through the sheet bundle 6 ateach of a plurality of binding positions while sandwiching the sheetbundle 6 from above and below sheet surfaces in the binding channel asillustrated in FIGS. 8 to 10. FIG. 8 is a perspective view of the sheetbinding engine 400 according to the embodiment. FIG. 9 is a plan view ofthe sheet binding engine 400 according to the embodiment. FIG. 10 is aside view, as viewed along the sub-scanning direction, of the sheetbundle 6 bound by the staple binding unit 420 according to theembodiment.

Upon completing sheet binding, the staple binding unit 420 returns tothe home position on the staple-binding-unit guide rail 421. Meanwhile,the sheet binding unit 4 according to the embodiment detects that thestaple binding unit 420 is on standby at the home position or hasreturned to the home position based on a result of detection of thestaple binding unit 420 by the staple-binding-unit detection sensor 422.

In a pre-sheet-binding phase, the stapleless binding unit 430 is onstandby at its home position. When sheet binding starts, the staplelessbinding unit 430 moves from the home position to a binding position onthe stapleless-binding-unit guide rail 431. The stapleless binding unit430 binds the sheet bundle 6 by compressing the sheet bundle 6 fromabove and below sheet surfaces in the binding channel having the shapeof an upper toothed jaw and a lower toothed jaw that can mesh with eachother as illustrated in FIG. 11. In the sheet bundle 6 compressed inthis manner, fibers of adjacent sheets are entangled at a bindingposition B illustrated in FIGS. 12 to 14, causing the sheet bindle 6 tobe bound. FIG. 11 illustrates side views, as viewed along themain-scanning direction, of the stapleless binding unit 430 according tothe embodiment FIG. 12 is a perspective view of the sheet binding engine400 according to the embodiment. FIG. 13 is a plan view of the sheetbinding engine 400 according to the embodiment. FIG. 14 is a side view,as viewed along the sub-scanning direction, of the sheet bundle 6 boundby the stapleless binding unit 430 according to the embodiment.

Upon completing sheet binding, the stapleless binding unit 430 returnsto the home position on the stapleless-binding-unit guide rail 431.Meanwhile, the sheet binding unit 4 according to the embodiment detectsthat the stapleless binding unit 430 is on standby at the home positionor has returned to the home position based on a result of detection ofthe stapleless binding unit 430 by the stapleless-binding-unit detectionsensor 432. Thus, in the embodiment, the staple binding unit 420 and thestapleless binding unit 430 function as “a plurality of binding units”which differ from each other in the maximum number of sheets that can bebound at a time by the binding unit.

The sheet support plate 440 supports the bottom surface of the sheetbundle 6 stacked in the compiling unit 410. The registration guides 450align the position of the sheet bundle 6 stacked in the compiling unit410 in the main-scanning direction.

The movable guide plate 460 pivots about the movable-guide-platepivot-support member 461. The movable guide plate 460 pivots such that aheight P of the movable guide plate 460 in the sheet thickness directionvaries depending on the maximum sheet count. More specifically, themovable guide plate 460 pivots such that the height P in the sheetthickness direction varies depending on by which one of the staplebinding unit 420 and the stapleless binding unit 430 the sheet bundle 6is to be bound.

This is described more specifically below. When the sheet bundle 6 is tobe bound by the staple binding unit 420, the sheet binding unit 4according to the embodiment causes the movable guide plate 460 to pivotso as to make the height P equal to or larger than the opening height L₁of the binding channel of the staple binding unit 420 as illustrated inFIG. 15. On the other hand, when the sheet bundle 6 is to be bound bythe stapleless binding unit 430, the sheet binding unit 4 according tothe embodiment causes the movable guide plate 460 to pivot so as to makethe height P equal to the opening height L₂ of the binding channel ofthe stapleless binding unit 430 as illustrated in FIG. 16. FIG. 15 is aside view, as viewed along the main-scanning direction, of the sheetbinding engine 400 according to the embodiment. FIG. 16 is a side view,as viewed along the main-scanning direction, of the sheet binding engine400 according to the embodiment. A feature of the sheet binding unit 4according to the embodiment lies in this operation of causing themovable guide plate 460 to pivot in this manner.

Hence, in the embodiment, the movable guide plate 460 functions as“stacked-sheet-count limiting unit” situated to move toward and awayfrom sheets held in the sheet tray in the sheet thickness direction andconfigured to limit the number of sheets held in the sheet tray byvarying the distance from a surface, which supports the sheets, of thesheet tray depending on the maximum sheet count of a selected one of theplurality of binding units.

The reason why the sheet binding unit 4 according to the embodimentcauses the height P to vary depending on the maximum sheet count or,more specifically, causes the movable guide plate 460 to pivot so as tovary the height P depending on by which one of the staple binding unit420 and the stapleless binding unit 430 the sheet bundle 6 is to bebound, is described below with reference to FIG. 17, FIG. 18, and FIG.19. FIG. 17 illustrates side views, as viewed along the main-scanningdirection, of the sheet binding engine 400 not including the movableguide plate 460 according to the embodiment. FIG. 18 illustrates sideviews, as viewed along the main-scanning direction, of the sheet bindingengine 400 not including the movable guide plate 460 according to theembodiment. FIG. 19 illustrates side views, as viewed along themain-scanning direction, of the sheet binding engine 400 according tothe embodiment.

When the sheet bundle 6 containing the first maximum sheet count ofsheets is to be bound using the staple binding unit 420 by the sheetbinding unit 4 not including the movable guide plate 460, the thicknessof the sheet bundle 6 does not exceed the opening height L₁ of thebinding channel of the staple binding unit 420. This is because theheight H of the compiling unit 410 in the sheet thickness direction isequal to the opening height L₁ of the binding channel as illustrated in(a) in FIG. 17. Accordingly, even when the sheet bundle 6 containing thefirst maximum sheet count of sheets is to be bound using the staplebinding unit 420, the sheet binding unit 4 not including the movableguide plate 460 can receive the sheet bundle 6 into the binding channelof the staple binding unit 420.

When the sheet bundle 6 containing sheets less than the first maximumsheet count is to be bound using the staple binding unit 420 by thesheet binding unit 4 not including the movable guide plate 460, aclearance in the sheet thickness direction is left in the compiling unit410. This is because the thickness of the sheet bundle 6 is smaller thanthe height H of the compiling unit 410 in the sheet thickness direction.Accordingly, in this case, curling, deflection, or the like can occur atthe binding position and increase the thickness of the sheet bundle 6equal to or larger than “should be thickness”.

However, the height H of the compiling unit 410 in the sheet thicknessdirection is equal to the opening height L₁ of the binding channel ofthe staple binding unit 420. For this reason, even if the curling ordeflection should occur, the thickness of the sheet bundle 6 does notexceed the opening height L₁ of the binding channel of the staplebinding unit 420 as illustrated in (b) in FIG. 17. Accordingly, evenwhen the sheet bundle 6 containing sheets less than the first maximumsheet count is to be bound using the staple binding unit 420, the sheetbinding unit 4 not including the movable guide plate 460 can receive thesheet bundle 6 into the binding channel of the staple binding unit 420.

When the sheet bundle 6 containing the second maximum sheet count ofsheets is to be bound using the stapleless binding unit 430 by the sheetbinding unit 4 not including the movable guide plate 460, a clearance inthe sheet thickness direction is left in the compiling unit 410. This isbecause the thickness of the sheet bundle 6 is smaller than the height Hof the compiling unit 410 in the sheet thickness direction. Accordingly,in this case, curling, deflection, or the like can occur at the bindingposition and increase the thickness of the sheet bundle 6 equal to orlarger than “should be thickness”.

When the thickness of the sheet bundle 6 is increased to be equal to orlarger than “should be thickness”, the thickness of the sheet bundle 6exceeds the opening height L₂ of the binding channel of the staplelessbinding unit 430 as illustrated in (a) in FIG. 18. This is because theopening height L₂ of the binding channel of the stapleless binding unit430 is smaller than the height H of the compiling unit 410 in the sheetthickness direction as described earlier. Accordingly, when the sheetbundle 6 containing the second maximum sheet count of sheets is to bebound using the stapleless binding unit 430, the sheet binding unit 4not including the movable guide plate 460 cannot receive the sheetbundle 6 into the binding channel of the stapleless binding unit 430,which is undesirable.

Similarly, when the sheet bundle 6 containing sheets less than thesecond maximum sheet count is to be bound using the stapleless bindingunit 430 by the sheet binding unit 4 not including the movable guideplate 460, a clearance in the sheet thickness direction is left in thecompiling unit 410. This is because the thickness of the sheet bundle 6is smaller than the height H of the compiling unit 410 in the sheetthickness direction. Accordingly, in this case, curling, deflection, orthe like can occur at the binding position and increase the thickness ofthe sheet bundle 6 equal to or larger than “should be thickness”.

When the thickness of the sheet bundle 6 is increased to be equal to orlarger than “should be thickness”, the thickness of the sheet bundle 6exceeds the opening height L₂ of the binding channel of the staplelessbinding unit 430 as illustrated in (b) in FIG. 18. This is because theopening height L₂ of the binding channel of the stapleless binding unit430 is smaller than the height H of the compiling unit 410 in the sheetthickness direction as described earlier. Accordingly, when the sheetbundle 6 containing sheets less than the second maximum sheet count isto be bound using the stapleless binding unit 430, the sheet bindingunit 4 not including the movable guide plate 460 cannot receive thesheet bundle 6 into the binding channel of the stapleless binding unit430, which is undesirable.

As described above, when the sheet bundle 6 is to be bound using thestaple binding unit 420, the sheet binding unit 4 not including themovable guide plate 460 can receive the sheet bundle 6 into the bindingchannel of the staple binding unit 420. However, when the sheet bundle 6is to be bound using the stapleless binding unit 430, an undesirablesituation where the sheet bundle 6 cannot be received into the bindingchannel of the stapleless binding unit 430 can occur.

To avoid this undesirable situation, as described above with referenceto FIGS. 15 and 16, the sheet binding unit 4 according to the embodimentis configured to cause the movable guide plate 460 to pivot to vary theheight P in the sheet thickness direction depending on the maximum sheetcount or, more specifically, to vary the height P in the sheet thicknessdirection depending on by which one of the staple binding unit 420 andthe stapleless binding unit 430 the sheet bundle 6 is to be bound.

This is described more specifically below. The sheet binding unit 4according to the embodiment is configured to cause, when the sheetbundle 6 is to be bound by the staple binding unit 420, the movableguide plate 460 to pivot so as to make the height P equal to or largerthan the opening height L₁ of the binding channel of the staple bindingunit 420 as illustrated in FIG. 15. On the other hand, the sheet bindingunit 4 according to the embodiment is configured to cause, when thesheet bundle 6 is to be bound by the stapleless binding unit 430, themovable guide plate 460 to pivot so as to make the height P equal to theopening height L₂ of the binding channel of the stapleless binding unit430 as illustrated in FIG. 16.

Hence, in the sheet binding unit 4 according to the embodiment, when thesheet bundle 6 is to be bound using the stapleless binding unit 430,even if the curling, deflection, or the like occurs due to a clearancethat is left in the thickness direction of sheets stacked in thecompiling unit 410, the thickness of the sheet bundle 6 does not exceedthe movable guide plate 460. As a result, when the sheet binding unit 4according to the embodiment performs sheet binding using the staplelessbinding unit 430, even if the curling, deflection, or the like occursdue to a clearance created in the thickness direction of sheets stackedin the compiling unit 410, the thickness of the sheet bundle 6 does notexceed the opening height L₂ of the binding channel of the staplelessbinding unit 430 as illustrated in FIG. 19. Accordingly, an undesirablesituation that the sheet bundle 6 cannot be received into the bindingchannel of the stapleless binding unit 430 will not occur.

Hence, the sheet binding unit 4 according to the embodiment can reliablyreceive the sheet bundle 6 even when the sheet bundle 6 is to be boundusing the stapleless binding unit 430 and the sheet binding unit 4 doesnot include compiling units independently, one for staple binding andthe other for stapleless binding. The sheet binding unit 4 according tothe embodiment can be inexpensively manufactured and perform sheetbinding with the compact and simple configuration.

Meanwhile, the sheet binding unit 4 according to the embodiment isconfigured to cause, when the sheet bundle 6 is to be bound using thestaple binding unit 420, the movable guide plate 460 to pivot so as tomake the height P equal to or larger than the opening height L₁ of thebinding channel of the staple binding unit 420 as described withreference to FIG. 15. Therefore, in the sheet binding unit 4 accordingto the embodiment, even when the sheet bundle 6 is to be bound using thestaple binding unit 420, the movable guide plate 460 does not interferewith sheet conveyance.

The closer the side, at which the height P is measured and which is theside opposite from the movable-guide-plate pivot-support member 461, ofthe movable guide plate 460 to the binding channel of the staplelessbinding unit 430, the greater the advantage of the embodiment of thesheet binding unit 4 according to the embodiment.

As described with reference to FIGS. 15 and 16, the example in which thesheet binding unit 4 according to the embodiment is configured to causethe movable guide plate 460 to pivot to vary the height P in the sheetthickness direction depending on the maximum sheet count has beendescribed. The sheet binding unit 4 according to the embodiment may bemodified to cause the movable guide plate 460 to pivot to vary theheight P in the sheet thickness direction depending on the number ofsheets to be bound at a time or, in other words, depending on the numberof sheets stacked in the compiling unit 410 to make up the sheet bundle6.

As described with reference to FIGS. 15 and 16, the example in which thesheet binding unit 4 according to the embodiment is configured to causethe movable guide plate 460 to pivot to vary the height P in the sheetthickness direction depending on the maximum sheet count has beendescribed. The sheet binding unit 4 according to the embodiment may bemodified such that the movable guide plate 460 is freely pivotable andpresses an uppermost sheet of the sheet bundle 6 stacked in thecompiling unit 410 under its own weight. The sheet binding unit 4according to the embodiment may be modified such that the movable guideplate 460 is freely pivotable within a range where the height P in thesheet thickness direction does not exceed the maximum sheet count andpresses the uppermost sheet of the sheet bundle 6 stacked in thecompiling unit 410 under its own weight.

This modification in which the movable guide plate 460 according to theembodiment is freely pivotable prevents, so long as the movable guideplate 460 is configured to be of a weight that will not hamper sheetconveyance, sheets from being damaged or stained by the movable guideplate 460.

As described with reference to FIG. 16, the example in which the sheetbinding unit 4 according to the embodiment is configured to cause themovable guide plate 460 to pivot to vary the height P in the sheetthickness direction depending on the maximum sheet count has beendescribed. Regarding when the movable guide plate 460 is to be pivoted,the movable guide plate 460 may be pivoted either before the sheets arestacked or after all the to-be-bound sheets are stacked.

In the embodiment, the example in which the image forming apparatus 1includes the image forming unit 2, the sheet feeding unit 3, the sheetbinding unit 4, and the scanner unit 5 has been described.Alternatively, a configuration in which the units are configured asindependent devices, and the devices are connected to each other to forman image forming system may be employed.

According to the embodiment described above, a sheet processing devicecapable of binding sheets without interfering with sheet conveyance withan inexpensive, compact, and simple configuration is provided.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A sheet processing device for binding a pluralityof sheets together, the sheet processing device comprising: a pluralityof binding units differing from each other in maximum sheet count, themaximum sheet count being a maximum number of sheets that can be boundat a time; a sheet tray configured to hold sheets until all to-be-boundsheets are placed therein, the number of the to-be-bound sheets being alargest one of the maximum sheet counts of the plurality of bindingunits or smaller; and a stacked-sheet-count limiting unit situated in athickness direction of the sheets held in the sheet tray, thestacked-sheet-count limiting unit being configured to limit the numberof sheets held in the sheet tray by varying a distance from a sheetsupport surface of the sheet tray on which the sheets are placed,depending on one of the binding units by which the plurality of sheetsheld in the sheet tray are to be bound.
 2. The sheet processing deviceaccording to claim 1, wherein the stacked-sheet-count limiting unit isconfigured to limit the number of sheets held in the sheet tray byvarying the distance depending on the maximum sheet count of the one ofthe binding units by which the plurality of sheets held in the sheettray are to be bound.
 3. The sheet processing device according to claim1, wherein the stacked-sheet-count limiting unit is configured to limitthe number of sheets held in the sheet tray by varying the distancedepending on the number of the to-be-bound sheets.
 4. The sheetprocessing device according to claim 1, wherein the stacked-sheet-countlimiting unit is configured to limit the number of sheets held in thesheet tray by varying the distance depending on the number of sheets tobe held in the sheet tray.
 5. The sheet processing device according toclaim 1, wherein the stacked-sheet-count limiting unit is configured tolimit the number of sheets held in the sheet tray by pressing, under itsown weight, the sheets held in the sheet tray in the thicknessdirection.
 6. The sheet processing device according to claim 1, whereineach of the binding units binds the plurality of sheets by a differentbinding scheme.
 7. The sheet processing device according to claim 1,wherein the plurality of binding units include a binding unit configuredto bind the plurality of sheets by a binding scheme with use of a stapleand a binding unit configured to bind the plurality of sheets by abinding scheme without use of a staple.
 8. An image forming systemcomprising: an image forming apparatus configured to form images on asheet; and the sheet processing device according to claim 1 to bind aplurality of sheets together, an image is formed on each sheet by theimage forming apparatus.